title: Regulation of the nitrate-reducing system enzymes in wild-type and mutant strains of Chlamydomonas reinhardii.
abstract: Six mutant strains (301, 102, 203, 104, 305, and 307) affected in their nitrate assimilation capability and their corresponding parental wild-type strains (6145c and 21gr) from Chlamydomonas reinhardii have been studied on different nitrogen sources with respect to NAD(P)H-nitrate reductase and its associated activities (NAD(P)H-cytochrome c reductase and reduced benzyl viologen-nitrate reductase) and to nitrite reductase activity. The mutant strains lack NAD(P)H-nitrate reductase activity in all the nitrogen sources. Mutants 301, 102, 104, and 307 have only NAD(P)H-cytochrome c reductase activity whereas mutant 305 solely has reduced benzyl viologen-nitrate reductase activity. Both activities are repressible by ammonia but, in contrast to the nitrate reductase complex of wild-type strains, require neither nitrate nor nitrite for their induction. Moreover, the enzyme from mutant 305 is always obtained in active form whereas nitrate reductase from wild-types needs to be reactivated previously with ferricyanide to be fully detected. Wild-type strains and mutants 301, 102, 104, and 307, when properly induced, exhibit an NAD(P)H-cytochrome c reductase distinguishable electrophoretically from constitutive diaphorases as a rapidly migrating band. Nitrite reductase from wild-type and mutant strains is also repressible by ammonia and does not require nitrate or nitrite for its synthesis. These facts are explained in terms of a regulation of nitrate reductase synthesis by the enzyme itself.
mesh_terms: D002696:Chlamydomonas / Q000235:genetics; D004790:Enzyme Induction; D009154:Mutation; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism; D009565:Nitrate Reductases / Q000235:genetics / Q000378:metabolism*; D009572:Nitrite Reductases / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism
chemical_list: D009251:NADPH-Ferrihemoprotein Reductase; D009565:Nitrate Reductases; D009572:Nitrite Reductases; D009584:Nitrogen